android imageView: setting drag and pinch zoom parameters

Question

I am currently developing for Android (my first app) an application which lets users see the subway map and be able to pinch zoom and drag around.

I am currently mod

Answer 1

Here is the complete code for pinch zoom and pan (Touch.java with some modifications that can be used practically)

public class Touch implements OnTouchListener {  

 // These matrices will be used to move and zoom image  
public static Matrix matrix = new Matrix();  
public static Matrix savedMatrix = new Matrix();  

 // We can be in one of these 3 states  
 static final int NONE = 0;  
 static final int DRAG = 1;  
 static final int ZOOM = 2;
private static final float MAX_ZOOM = (float) 3;
private static final float MIN_ZOOM = 1;  
 int mode = NONE;  

 // Remember some things for zooming  
 PointF start = new PointF();  
 PointF mid = new PointF();  
 float oldDist = 1f;  

 int width,height;

 @Override  
 public boolean onTouch(View v, MotionEvent event) {


  ImageView view = (ImageView) v;
  Rect bounds = view.getDrawable().getBounds();

  width = bounds.right - bounds.left;
  height = bounds.bottom - bounds.top;
  // Dump touch event to log  
  dumpEvent(event);  

  // Handle touch events here...  
  switch (event.getAction() & MotionEvent.ACTION_MASK) {  
  case MotionEvent.ACTION_DOWN:  
   savedMatrix.set(matrix);  
   start.set(event.getX(), event.getY());  
   mode = DRAG;  
   break;  
  case MotionEvent.ACTION_POINTER_DOWN:  
   oldDist = spacing(event);  
   if (oldDist > 10f) {  
    savedMatrix.set(matrix);  
    midPoint(mid, event);  
    mode = ZOOM;  
   }  
   break;  
  case MotionEvent.ACTION_UP:  
  case MotionEvent.ACTION_POINTER_UP:  
   mode = NONE;  
   break;  
  case MotionEvent.ACTION_MOVE:  
   if (mode == DRAG) {  
    // ...      
    matrix.set(savedMatrix);  
    matrix.postTranslate(event.getX() - start.x, event.getY() - start.y);      
   } else if (mode == ZOOM) {  
    float newDist = spacing(event);  
    if (newDist > 10f) {  
     matrix.set(savedMatrix);  
     float scale = newDist / oldDist;  
     matrix.postScale(scale, scale, mid.x, mid.y);  
    }  
   }  
   break;  
  }  
//----------------------------------------------------
  limitZoom(matrix);
  limitDrag( matrix);
//----------------------------------------------------  
  view.setImageMatrix(matrix);  
  return true; // indicate event was handled  
 }  

 /** Show an event in the LogCat view, for debugging */  
 private void dumpEvent(MotionEvent event) {  
  String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",  
    "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };  
  StringBuilder sb = new StringBuilder();  
  int action = event.getAction();  
  int actionCode = action & MotionEvent.ACTION_MASK;  
  sb.append("event ACTION_").append(names[actionCode]);  
  if (actionCode == MotionEvent.ACTION_POINTER_DOWN  
    || actionCode == MotionEvent.ACTION_POINTER_UP) {  
   sb.append("(pid ").append(  
     action >> MotionEvent.ACTION_POINTER_ID_SHIFT);  
   sb.append(")");  
  }  
  sb.append("[");  
  for (int i = 0; i < event.getPointerCount(); i++) {  
   sb.append("#").append(i);  
   sb.append("(pid ").append(event.getPointerId(i));  
   sb.append(")=").append((int) event.getX(i));  
   sb.append(",").append((int) event.getY(i));  
   if (i + 1 < event.getPointerCount())  
    sb.append(";");  
  }  
  sb.append("]");  
 }  

 /** Determine the space between the first two fingers */  
 private float spacing(MotionEvent event) {  
  float x = event.getX(0) - event.getX(1);  
  float y = event.getY(0) - event.getY(1);  
  return FloatMath.sqrt(x * x + y * y);  
 }  

 /** Calculate the mid point of the first two fingers */  
 private void midPoint(PointF point, MotionEvent event) {  
  float x = event.getX(0) + event.getX(1);  
  float y = event.getY(0) + event.getY(1);  
  point.set(x / 2, y / 2);  
 }  

 private void limitZoom(Matrix m) {

        float[] values = new float[9];
        m.getValues(values);
        float scaleX = values[Matrix.MSCALE_X];
        float scaleY = values[Matrix.MSCALE_Y];
        if(scaleX > MAX_ZOOM) {
            scaleX = MAX_ZOOM;
        } else if(scaleX < MIN_ZOOM) {
            scaleX = MIN_ZOOM;
        }

        if(scaleY > MAX_ZOOM) {
            scaleY = MAX_ZOOM;
        } else if(scaleY < MIN_ZOOM) {
            scaleY = MIN_ZOOM;
        }

        values[Matrix.MSCALE_X] = scaleX;
        values[Matrix.MSCALE_Y] = scaleY; 
        m.setValues(values);
    }


 private void limitDrag(Matrix m) {

        float[] values = new float[9];
        m.getValues(values);
        float transX = values[Matrix.MTRANS_X];
        float transY = values[Matrix.MTRANS_Y];
        float scaleX = values[Matrix.MSCALE_X];
        float scaleY = values[Matrix.MSCALE_Y];
//--- limit moving to left ---
        float minX = (-width + 0) * (scaleX-1); 
        float minY = (-height + 0) * (scaleY-1);
//--- limit moving to right ---     
        float maxX=minX+width*(scaleX-1);
        float maxY=minY+height*(scaleY-1);
        if(transX>maxX){transX = maxX;}
        if(transXmaxY){transY = maxY;}
        if(transY